This invention is directed to a ventilated cage and rack system, and more particularly to an open rack system which provides protection for both personnel attending to the system and animals contained within the cage from contamination by reducing cross cage contamination.
Ventilated cage and rack systems are well known in the art. One such ventilated cage and rack system is disclosed in U.S. Pat. No. 4,365,590 assigned to Lab Products, Inc. in which a closed rack system including a plurality of shelves each having a door for each shelf is provided. Each shelf compartment is sized to contain horizontally spaced animal cages having open top ends spaced well below the ceiling of the shelf compartment. A low pressure air plenum extends along one side of the rack system to provide air to each of the shelves. The opposed side of each shelf has filtered air port openings which communicate with the room interior to provide a low pressure negative air flow across the top open ends of the animal cages. This cage and rack system also provides a watering system in which a water valve connected to a common water manifold extends into the cage to allow animals to drink therefrom.
The prior art ventilated cage and rack system was satisfactory. However, it suffered from the deficiencies that it can not provide a cage level barrier as the barrier was breached by the insertion of the valve coupled to the main watering system each time the cage was removed from the rack system and then re-inserted into the rack system. Additionally, the air flow for a single cage could not be controlled. Accordingly, inadequate personnel protection is provided by this ventilated cage and rack system.
One such solution to the cage barrier problem was to provide a quick disconnect valve within the ventilated cage and rack system so that the cage and the drinking valve could be disconnected from the rack while making it possible to maintain the drinking valve within the same cage at all times, thus preventing cross contamination due to reinsertion of the drinking valve. Additionally, a positive air pressure plenum provides positive air pressure through the cage in addition to the negative air flow across the tops of the cages.
This ventilated cage and rack system was also satisfactory. However, it also suffered from the disadvantage that no personnel protection was provided when the rack doors were opened. Furthermore, it was found that to provide the negative air plenum and positive air plenum that a great deal of air was required to move an air column along the large space between the cage top and the bottom of the next highest shelf. Accordingly, amounts of energy and high air velocities were required to move the column of air across the cage tops.
The cages used in the prior art system have a filtered top and gas impermeable bottom which are closed in a petri dish manner. The top is formed with a lip which rests on and overhangs the bottom. A wire bar lid is disposed between the top and bottom to contain the animal in the cage as well as hold a water bottle and/or feed in an animal accessible position. The conventional lid includes a wire frame having a circular cross-section with lateral wire rods welded to the frame, creating a 1/4 inch gap between the filter top and cage bottom. Air passes through the gap created at the meeting point of this top and bottom letting contaminated air out and letting outside air within the cage. However, when a positive pressure air flow is provided within the cage this gap allows bedding and debris to be discharged from the cage by the activity of the animals contained with the cage. Accordingly, cross contamination can occur when two cages are positioned adjacent each other on the shelf. Additionally, personnel contamination occurs as the contaminated gases pass from the cages to the rack.
One attempt to cure this cross contamination problem is known in U.S. Pat. No. 4,343,261 in which all air flow is directed entirely through the filter of a cage top positioned in the rack. However, this cage and rack system suffers from the disadvantage of forcing contaminants disposed on the filter top into the cage.
Accordingly, it is desired to provide a ventilated cage and rack system which overcomes the shortcomings of the prior art by combining both personnel proteotion and animal protection at a cage level barrier while decreasing the volume of air and energy required to do so.